Advances in the development of thin-film transistors (TFT) have facilitated the commercialization of active matrix liquid crystal displays enabling notebook PCs, and flat screen TVs and monitors. In parallel with flat rigid glass substrates based on TFT technology, there is also a growing interest in flexible TFT backplanes for both large and small area electronics, such as for display, imaging, sensor, photovoltaic and RFID applications.
Thin plastic substrates are the primary candidates for flexible substrates. Polyester films such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) from DuPont Teijin Film (DTF) are well-known substrates for a wide range of electronic applications. PEN-based substrates offer excellent dimensional stability, low moisture pickup, good solvent resistance, high clarity, and very good surface smoothness. Most flexible substrates (for example, those made of polyethylene naphthalates or polyimides), however, are too thin to be handled freestanding in standard microelectronic or semiconductor machines and tools. This creates a need for a means to permit temporary bonding of the flexible substrate to a rigid carrier as the flexible substrate is moved through the tools, machines, ovens, and cleaning devices used in fabrication processes.
Laminating adhesives that permit temporary bonding of flexible substrates and that will not compromise handling or performance of the substrates would facilitate the rapidly growing demand for flexible electronics. Development of such adhesives would allow existing fabrication methods, such as for semiconductors, active matrix thin film transistors, or photovoltaics, to use the currently installed base of manufacturing tools and machines.
Such laminating adhesives used in electronics fabrication processes must maintain adhesion at temperatures equal to or greater than 200° C. and at vacuum conditions of 10−6 mmHg for several hours without deformation or defects. In one embodiment, the adhesives must maintain adhesion at temperatures equal to or greater than 150° C. Most currently available laminating adhesives are not thermally stable and cannot survive the maximum processing temperatures of the manufacturing steps. To address these issues, the inventors have found certain resin combinations suitable for high temperature temporary bonding applications.